Joe Lieberman: It is REALLY Time for the Democrats to Cut Him Loose
If Lieberman endorses a Republican the Dems should immediately strip him of any and all committee assignments, deprive him of any political or financial support in future campaigns, and in every other possible way treat him as anathema. In fact, they should make it clear that they will do everything necessary to defeat Lieberman in 2012.
The Democrats can't get any legislation through the Senate as it is, so there is nothing to lose. Apparently that is what it takes to get the Dems to act like they have a spine.
P.S.: (Added 17 December) Here is the story from The New York Times confirming Liberman's endorsement.